Inductor structure having embedded airgap

ABSTRACT

Various embodiments include inductor structures including at least one air gap for reducing capacitance between windings in the inductor structure. One embodiment includes an inductor structure having: a substrate; an insulation layer overlying the substrate; a conductive winding overlying the substrate within the insulation layer, the conductive winding wrapped around itself to form a plurality of turns substantially concentric about a central axis; an insulating structural support containing an air gap between the conductive winding and the insulation layer, the insulating structural support at least one of under, over or surrounding the plurality of turns of the conductive winding or between adjacent turns in the conductive winding; and at least one insulation pocket located radially inside a radially innermost turn in the plurality of turns with respect to the central axis.

FIELD

The subject matter disclosed herein relates to integrated circuits. Moreparticularly, the subject matter relates to inductor structure andmethods of forming such structures.

BACKGROUND

Conventional inductor structures include conductive wires, each formedin a series of windings that is wrapped around itself. The wire isformed over a substrate within an insulation material (e.g. silicondioxide (SiO₂)) layer to insulate the wire from its adjacent winding.Inductor structures may include multi-level (multi-line) structuresconnected by one or more vias (inter-level connectors). Conventionalinductor structures experience winding capacitance effects which canaffect the quality factor (Q) of the structure.

BRIEF DESCRIPTION

Various embodiments include inductor structures including at least oneair gap for reducing capacitance between windings in the inductorstructure. An air gap is formed when a sacrificial material, such issilicon, is embedded on a wafer and is subsequently removed andoptionally hermetically sealed, leaving a cavity. Some particularembodiments include an inductor structure having: a substrate; aninsulation layer overlying the substrate; a conductive winding overlyingthe substrate within the insulation layer, the conductive windingwrapped around itself to form a plurality of turns substantiallyconcentric about a central axis; an insulating structural supportcontaining an air gap between the conductive winding and the insulationlayer, the insulating structural support at least one of under, over orsurrounding the plurality of turns of the conductive winding or betweenadjacent turns in the conductive winding; and at least one insulationpocket located radially inside a radially innermost turn in theplurality of turns with respect to the central axis.

A first aspect includes an inductor structure having: a substrate; aninsulation layer overlying the substrate; a conductive winding overlyingthe substrate within the insulation layer, the conductive windingwrapped around itself to form a plurality of turns substantiallyconcentric about a central axis; an insulating structural supportcontaining an air gap between the conductive winding and the insulationlayer, the insulating structural support at least one of under, over orsurrounding the plurality of turns of the conductive winding or betweenadjacent turns in the conductive winding; and at least one insulationpocket located radially inside a radially innermost turn in theplurality of turns with respect to the central axis.

A second aspect includes an inductor structure having: a substrate; aninsulation layer overlying the substrate; a first conductive windingoverlying the substrate within the insulation layer, the firstconductive winding wrapped around itself to form a first plurality ofturns substantially concentric about a central axis; a second conductivewinding overlying the first conductive winding within the insulationlayer, the second conductive winding wrapped around itself to form asecond plurality of turns substantially concentric about the centralaxis; an insulating structural support containing an air gap between thesecond conductive winding and at least one of the insulation layer orthe first conductive winding, the insulating structural support at leastone of under, over or surrounding the plurality of turns of the secondconductive winding or between adjacent turns in the second conductivewinding; and at least one insulation pocket located radially inside aradially innermost turn in the plurality of turns of the secondconductive winding with respect to the central axis.

A third aspect includes an inductor structure having: a substrate; aninsulation layer overlying the substrate; a conductive winding overlyingthe substrate within the insulation layer, the conductive windingwrapped around itself to form a plurality of turns substantiallyconcentric about a central axis; an insulating structural supportcontaining an air gap between the conductive winding and the insulationlayer, the insulating structural support at least one of under, over orsurrounding the plurality of turns of the conductive winding or betweenadjacent turns in the conductive winding; and a plurality of insulationpockets located radially inside a radially innermost turn in theplurality of turns with respect to the central axis, wherein theconductive winding has a line width of approximately one micrometer toone hundred micrometers, and wherein each of the plurality of insulationpockets extends from a bottom of the conductive winding beyond a top ofthe conductive winding by approximately 2 micrometers to approximately 6micrometers measured in a direction parallel with the central axis.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will be more readilyunderstood from the following detailed description of the variousaspects of the invention taken in conjunction with the accompanyingdrawings that depict various embodiments of the invention, in which:

FIG. 1 shows a schematic perspective view of an inductor structureaccording to various embodiments.

FIG. 2 shows a schematic perspective view of an inductor structureaccording to various additional embodiments.

FIG. 3 shows a schematic perspective view of an inductor structureaccording to various additional embodiments.

FIG. 4 shows a schematic cross-sectional depiction of one optionalportion of the inductor structure of FIG. 3 according to variousembodiments.

FIG. 5 shows a schematic cross-sectional depiction of a first optionalportion of the inductor structures of FIG. 1 and/or FIG. 2 according tovarious embodiments.

FIG. 6 shows a schematic cross-sectional depiction of a second optionalportion of the inductor structures of FIG. 1 and/or FIG. 2 according tovarious embodiments.

It is noted that the drawings of the invention are not necessarily toscale. The drawings are intended to depict only typical aspects of theinvention, and therefore should not be considered as limiting the scopeof the invention. In the drawings, like numbering represents likeelements between the drawings.

DETAILED DESCRIPTION

As noted, the subject matter disclosed herein relates to integratedcircuits. More particularly, the subject matter relates to inductorstructures including capacitance-modifying air gaps.

As described herein, conventional inductor structures experience windingcapacitance effects which can affect the quality factor (Q) of thestructure. In contrast to these conventional inductor structures,various embodiments include inductor structures including at least oneinsulating structural support containing an air gap (or, pocket) above,below, around and/or between winding(s) to reduce winding capacitance inthe structure, thereby improving the quality factor (Q). These inductorstructures can also experience improved useful bandwidth when comparedwith conventional inductor structures. In some particular cases, with asingle level inductor quality factor can be improved by approximately 10percent, with useful bandwidth improved by approximately 20 percent.

As described herein an air gap is formed in the inductor structuresaccording to various embodiments, when a sacrificial material, such issilicon, is embedded on a wafer and is subsequently removed andoptionally hermetically sealed, leaving a cavity. It is understood that,although the term air gap is used, in reality, there are residual gasesfrom the sealing process in the cavity which can be at less thanatmospheric pressure. If, according to various embodiments, the cavityis sealed off using plasma enhanced silicon dioxide using oxygen andsilane as gas precursors at a pressure of 10 Torr, then there could beoxygen in the sealed cavity at a pressure of approximately 10 Torr.

Various particular embodiments include an inductor structure having: asubstrate; an insulation layer overlying the substrate; a conductivewinding overlying the substrate within the insulation layer, theconductive winding wrapped around itself to form a plurality of turnssubstantially concentric about a central axis; an insulating structuralsupport containing an air gap between the conductive winding and theinsulation layer, the insulating structural support at least one ofunder, over or surrounding the plurality of turns of the conductivewinding or between adjacent turns in the conductive winding; and atleast one insulation pocket located radially inside a radially innermostturn in the plurality of turns with respect to the central axis. It isunderstood that according to various embodiments, the insulation layershown and described herein may not be necessary, as the substrate mayinclude an insulating layer and/or insulating properties.

Other particular embodiments include an inductor structure having: asubstrate; an insulation layer overlying the substrate; a firstconductive winding overlying the substrate within the insulation layer,the first conductive winding wrapped around itself to form a firstplurality of turns substantially concentric about a central axis; asecond conductive winding overlying the first conductive winding withinthe insulation layer, the second conductive winding wrapped arounditself to form a second plurality of turns substantially concentricabout the central axis; an insulating structural support containing anair gap between the second conductive winding and at least one of theinsulation layer or the first conductive winding, the insulatingstructural support at least one of under, over or surrounding theplurality of turns of the second conductive winding or between adjacentturns in the second conductive winding; and at least one insulationpocket located radially inside a radially innermost turn in theplurality of turns of the second conductive winding with respect to thecentral axis.

Additional particular embodiments include an inductor structure having:a substrate; an insulation layer overlying the substrate; a conductivewinding overlying the substrate within the insulation layer, theconductive winding wrapped around itself to form a plurality of turnssubstantially concentric about a central axis; an insulating structuralsupport containing an air gap between the conductive winding and theinsulation layer, the insulating structural support at least one ofunder, over or surrounding the plurality of turns of the conductivewinding or between adjacent turns in the conductive winding; and aplurality of insulation pockets located radially inside a radiallyinnermost turn in the plurality of turns with respect to the centralaxis, wherein the conductive winding has a line width of approximatelyone micrometer to approximately one hundred micrometers, and whereineach of the plurality of insulation pockets extends from a bottom of theconductive winding beyond a top of the conductive winding byapproximately 2 micrometers to approximately 6 micrometers measured in adirection parallel with the central axis.

In the following description, reference is made to the accompanyingdrawings that form a part thereof, and in which is shown by way ofillustration specific exemplary embodiments in which the presentteachings may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice thepresent teachings and it is to be understood that other embodiments maybe utilized and that changes may be made without departing from thescope of the present teachings. The following description is, therefore,merely exemplary.

FIG. 1 shows a schematic perspective view of an inductor structure 10according to various embodiments. As shown, the inductor structure 10can include a substrate 12, e.g., at least one of silicon (Si) orsilicon dioxide (SiO₂). Overlying the substrate 12 is an insulationlayer 14 (e.g., including SiO₂ glass), which insulates adjacent layersof a conductive winding 16 overlying the substrate 12 and located withinthe insulation layer 14. The conductive winding 16 can be formed of anyconventional conductive winding material, e.g., tungsten (W), copper(Cu) and/or an aluminum-based compound (e.g., Al—Cu).

The conductive winding 16 is wrapped around itself to form a pluralityof turns (windings) 18 that are substantially concentric about a centralaxis (z). The central axis (z) is used as a reference point herein todelineate various aspects, however, it is understood that otherreference point(s) may be used to describe various components of theinductor structures described.

In contrast to conventional inductor structures, the inductor structure10 of FIG. 1 includes an insulating structural support 20 containing anair gap (several shown) 22 between the conductive winding 16 and theinsulation layer 14. The insulating structural support 20 (containingthe air gap 22) can be located at least one of under, over orsurrounding the turns 18 of the conductive winding 16, or can be locatedbetween adjacent turns 18 of the conductive winding 16. According tovarious embodiments, the air gap 22 can be formed as a contained pocketof air within an the insulating structural support 20, which can includean oxide liner, including an oxide such as one or more of silicondioxide (SiO₂), P-doped SiO₂, B-doped SiO₂, F-doped SiO₂, SiCOH, SiN,SiC, SiCN, Al₂O₃, Ta₂O₅, or any other dielectrics that areconventionally used in semiconductor wafer processing. The insulatingstructural support 20 (liner) can be deposited using any conventionalmethod, such as chemical vapor deposition (CVD), plasma-enhanced CVD(PECVD), atomic layer CVD (ALD), high density plasma CVD (HDPCVD),thermal CVD (THCVD), sub-atmospheric CVD (SACVD), and the like. The airgap 22 can help to reduce capacitance between turns 18 (e.g., adjacentturns 18) of the conductive winding when compared with SiO₂. As notedherein, the air gap 22 is contained within the insulating structuralsupport 20 (e.g., an oxide liner), which resides within the insulationlayer 14, such that the insulating structural support 20 and theinsulation layer 14 provide an air-tight seal on the air gap 22.

Also shown, the inductor structure 10 can include at least oneinsulation pocket 24 (several shown) located radially inside a radiallyinnermost turn 26 in the plurality of turns 18 with respect to thecentral axis (z). According to various embodiments, the insulationpocket(s) 24 can be formed of an oxide such as those oxides notedherein, and can contain an air gap 28. As noted herein, the air gap 28is contained within the insulation pocket 24, such that the insulationpocket 24 provides an air-tight seal on the air gap 28. The insulationpocket 24 may be substantially hollow, such that the air gap 28 occupiesmost of the internal volume in the insulation pocket 24.

In various embodiments, the inductor structure 10 can include aplurality of insulation pockets 24 symmetrically dispersed about thecentral axis (z). As shown, in some cases, each of the plurality ofturns 18 can include a set of substantially straight sections 30 betweeneach of a set of bends 32. In various embodiments, e.g., as shown inFIG. 1, the air gap 22 can span approximately 45 percent toapproximately 90 percent of a length (L) of at least one of thesubstantially straight sections 30.

In other embodiments, as shown in the schematic depiction of alternativeinductor structure 110 in FIG. 2, the insulating structural support 20(containing air gap 22) can span approximately 66 percent toapproximately 90 percent of a length of the at least one of thesubstantially straight sections 30. With reference to both inductorstructure 10 (FIG. 1) and alternative inductor structure 110 (FIG. 2),the insulation pocket(s) 24 can have a substantially trapezoidal shape(tapered radially inward) with a first base 36 having a first length anda second base 38 having a second length greater than the first length.The second length (second base 38) can span approximately 75 percent toapproximately 85 percent of the length (L) of the substantially straightsection 30.

According to various embodiments, the conductive winding 16 has a linewidth of approximately one micrometer to approximately one hundredmicrometers. In these cases, each of the plurality of insulation pockets24 extends from a bottom of the conductive winding 16 beyond a top ofthe conductive winding 16 by approximately 2 micrometers toapproximately 6 micrometers measured in a direction parallel with thecentral axis (z).

FIG. 3 shows a three-dimensional perspective view of another inductorstructure 210, including air gaps 22 and oxide pockets 24 as shown anddescribed with reference to FIG. 1 and FIG. 2. The inductor structure210 of FIG. 3 can include a multi-level inductor structure, includingtwo distinct wiring (conductive winding) layers. As shown, the inductorstructure 210 can include a substrate 12, an insulation layer 14overlying the substrate, and a first conductive winding 16 overlying thesubstrate 12 and located within the insulation layer 14. As notedherein, the conductive winding 16 can be formed of any conventionalconductive winding material, e.g., tungsten (W), copper (Cu) and/or analuminum-based compound (e.g., Al—Cu).

The inductor structure 210 can also include a second conductive winding216 overlying the first conductive winding 16 within the insulationlayer 14. Similar to the first conductive winding 16, the secondconductive winding 216 can be formed of any conventional conductivewinding material, e.g., tungsten (W), copper (Cu) and/or analuminum-based compound (e.g., Al—Cu). Further, as noted herein withrespect to the first conductive winding 16, the second conductivewinding 216 is wrapped around itself to form a second plurality of turns218 substantially concentric about the central axis (z). As shown, theinductor structure 210 can also include an insulating structural support20 containing an air gap 22 between the second conductive winding 216and at least one of the insulation layer 14 or the first conductivewinding 16. The insulating structural support 20 (containing air gap 22)is located at least one of under, over or surrounding the plurality ofturns 218 of the second conductive winding 216, or, the insulatingstructural support 20 (containing air gap 22) is located betweenadjacent turns 218 in the second conductive winding 216.

Similarly to the inductor structure 10 shown and described withreference to FIG. 1, the inductor structure 210 can include at least oneinsulation pocket 24 (several shown) located radially inside a radiallyinnermost turn 26 in the plurality of turns 18 with respect to thecentral axis (z). The insulation pocket 24 can include an air gap 28 asdescribed herein.

According to various embodiments, the first conductive winding and thesecond conductive winding 216 each have a line width of approximatelyone micrometer to approximately one hundred micrometers. In these cases,each of the plurality of insulation pockets 24 extends from a bottom ofthe first conductive winding 16 beyond a top of the second conductivewinding 216 by approximately 1 micrometer to approximately 2 micrometersmeasured in a direction parallel with the central axis (z).

FIG. 4 shows a schematic cross-sectional depiction of one optionalportion of the inductor structure 210, according to various embodiments.This cross-section is taken through one of the air gaps in a straightsection 30 (FIG. 3) of the plurality of turns 18. In this embodiment,the insulating structural support 20 containing the air gap 22substantially surrounds both the first conductive winding 16 and thesecond conductive winding 216. Additionally, the air gap 22 extendsbetween adjacent turns 218 in the second conductive winding.

Several methods may be used to fabricate the structure shown in FIG. 4.One method can include encapsulating at least one of the turns 18 andthe insulation material 14 in a sacrificial material, such as silicon.The sacrificial silicon, which will occupy the regions labeled as theair gap 22 before being removed, is formed using any known methodincluding reverse damascene, and can be removed from vent holes using,e.g., XeF₂ gas. The gaps (vent holes) left after removal of thesacrificial silicon can then be optionally hermetically sealed using asequential oxide and nitride deposition, as known in the art.

In various embodiments, a method of forming at least one cavity (e.g.,air gap 22) can include: forming a first sacrificial cavity layer over alower wiring layer; forming a layer; forming a second sacrificial layerover the first sacrificial layer and in contact with the layer; forminga lid on the second sacrificial cavity layer; forming at least one venthole in the lid, exposing a portion of the second sacrificial cavitylayer; venting or stripping the second sacrificial cavity layer suchthat a top surface of the second sacrificial cavity layer is no longertouching a bottom surface of the lid, before venting or stripping thefirst sacrificial cavity layer, thereby forming a first cavity and asecond cavity, respectively.

FIG. 5 shows a schematic cross-sectional depiction of a first optionalportion of the inductor structures 10 and/or 110 according to variousembodiments. This cross-section is taken through one of the air gaps 22in a straight section 30 (FIG. 1, FIG. 2) of the plurality of turns 18.In this embodiment, the air gap 22 substantially surrounds the firstconductive winding.

FIG. 6 shows a schematic cross-sectional depiction of a second optionalportion of the inductor structures 10 and/or 110 according to variousembodiments. This cross-section is taken through one of the air gap 22in a straight section 30 (FIG. 1, FIG. 2) of the plurality of turns 18.In this embodiment, the air gap 22 substantially surrounds the firstconductive winding. Additionally, the air gap 22 extends betweenadjacent turns 18 in the conductive winding 16.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a”, “an” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on”, “engaged to”,“connected to” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto”, “directly connected to” or “directly coupled to” another element orlayer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Spatially relative terms, such as “inner,” “outer,” “beneath”, “below”,“lower”, “above”, “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

The foregoing description of various aspects of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and obviously, many modifications and variations arepossible. Such modifications and variations that may be apparent to anindividual in the art are included within the scope of the invention asdefined by the accompanying claims.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

We claim:
 1. An inductor structure comprising: a substrate; aninsulation layer overlying the substrate; a first conductive windingoverlying the substrate within the insulation layer, the firstconductive winding wrapped around itself to form a first plurality ofturns substantially concentric about a central axis; a second conductivewinding overlying the first conductive winding within the insulationlayer, the second conductive winding wrapped around itself to form asecond plurality of turns substantially concentric about the centralaxis; an insulating support structure containing an air gap between thesecond conductive winding and at least one of the insulation layer orthe first conductive winding, the insulating support structure at leastone of under, over or surrounding the plurality of turns of the secondconductive winding or between adjacent turns in the second conductivewinding; and at least one insulation pocket located radially inside aradially innermost turn in the plurality of turns of the secondconductive winding with respect to the central axis.
 2. The inductorstructure of claim 1, wherein the at least one insulation pocketcontains a second air gap.
 3. The inductor structure of claim 1, whereinthe at least one insulation pocket includes a plurality of insulationpockets symmetrically dispersed about the central axis.
 4. The inductorstructure of claim 1, wherein the air gap reduces a capacitance betweenadjacent turns in the plurality of turns in the second conductivewinding.
 5. The inductor structure of claim 1, wherein each of theplurality of turns in the second conductive winding includes a set ofsubstantially straight sections between each of a set of bends.
 6. Theinductor structure of claim 5, wherein the insulating support structurecontaining the air gap spans approximately 45 percent to approximately90 percent of a length of at least one of the substantially straightsections.
 7. The inductor structure of claim 5, wherein the insulatingsupport structure containing the air gap spans approximately 66 percentto approximately 90 percent of a length of the at least one of thesubstantially straight sections.
 8. The inductor structure of claim 5,wherein the insulation pocket has a substantially trapezoidal shape witha first base having a first length and a second base have a secondlength greater than the first length, wherein the second length spansapproximately 75 percent to approximately 85 percent of a length of theat least one of the substantially straight sections.